1. Field of the Invention
The present invention generally relates to fuses included within semiconductor structures which protect semiconductor devices from excessive voltage and/or current or which selectively and permanently connect/disconnect semiconductor devices from one another.
2. Description of the Related Art
As the size and voltage/current ratings of semiconductor devices becomes smaller, as a result of device miniaturization, the fuses which protect or disconnect such devices must be opened (“blown”) with smaller amounts of energy to accommodate the delicacy of todays semiconductor products. In an effort to reduce and/or eliminate the damage caused to the product when the fuses are blown, designers have been patterning fuses in various manners to solve this problem and to reduce costs as well.
There are several kinds of integrated circuit applications that require some form of electrically programmable memory for storing information. The information stored varies significantly in size ranging from a few bits used to program simple identification data, to several megabits used to program computer programs. Fabricating these types of memory devices along with core logic integrated circuitry adds a number of additional processing steps that significantly raise product costs. Usually, the additional product costs are difficult to justify when only relatively small amounts of electrically programmable elements are needed for a particular integrated circuit application.
As such, in order to reduce costs, semiconductor designers have been implementing “fuse” structures that are made out of existing doped polysilicon layers that are typically patterned to define transistor gates over a semiconductor structure. Once formed, the fuse structure may be “programmed” by passing a sufficiently high current that melts and vaporizes a portion of the polysilicon fuse. In the programmed state, the fuse structure typically has a resistance that is substantially greater than the non-programmed state, thereby producing an open circuit. This is of course counter to antifuse devices that become short circuits (i.e., substantially decreased resistance) in a programmed state. Although traditional fuse structures work well, they typically consume a large amount of power in programming that may make them unfit for a variety of low power integrated circuit products.
Current back end fuses are made of aluminum or copper and formerly were made of tungsten. Polysilicon is used in the front end of the chip which can tolerate high temperatures (this is the device end not the interconnect end).
Currently, fuses are made in semiconductors within the chip. However, the prior art is bereft of devices in which fuses are plated at the uppermost level. Moreover, the prior art is devoid of devices in which a damascene process is used to form the fuse structure at the uppermost level. Because softer and inherently weaker materials that will pass oxygen through them are beginning to be used by designers and manufacturers, there is a need to create easily fabricated fuses that will not damage the product when they are blown.